Such apparatus is known from a publication of P. Klauer, M. A. Rückert, P. Vogel, W. H. Kullmann, P. M. Jakob, V. C. Behr, Proc. Intl. Soc. Mag. Res. Med. 2011, 19, 3783 (see Reference [8] below).
Brief Introduction to MPI
Magnetic Particle Imaging (MPI) is a new ultra-fast tracer-based imaging technology with promising applications particularly in cardio-vascular research and diagnosis.
In MPI, contrast agent such as Super-Paramagnetic Iron Oxide Nano-Particles (SPIOs) are exposed to a magnetic field (Drive Field) that oscillates in 1-3 spatial dimensions. The non-linear magnetization change of these particles generates an electromagnetic signal which contains contributions at higher harmonics of the excitation signal. This signal can be detected by suitable detection coils and an image can be reconstructed. A strong gradient field (Selection Field, SF) saturates the particle magnetization everywhere except for a small Field Free Region (=FFR), thereby confining the signal generation to this region. The Drive Field shifts this FFR in space, and the passage of the FFR over the Super-Paramagnetic Iron Oxide Nano-Particles induces the aforementioned non-linear magnetization change. The topology of the Field Free Region can be either a point (Field Free Point, FFP scanners) or a line (Field Free Line, FFL scanners) depending on the layout of the Selection Field. The advantage of FFL scanners is that they obtain signal from a larger volume at each instant of time, thereby achieving a higher SNR. As the signal at a given point of time comes from particles in multiple positions along the FFL, the encoding scheme must sample each object position with different FFL orientations to allow unambiguous image reconstruction.